Effects Of Modified Atmospheric Packaging And Pretreatments On The Quality Of Fresh Pork During Its Shelf-life

This study is focused on the modified atmospheric packaging (MAP) and theapplication of the pretreatments of lactic acid, ascorbic acid and oxygenation toimprove the quality during shelf life of the fresh meat, and on the comparison betweenconventional postmortem stored and early postmortem stored fresh meat packaging inthe modified atmosphere. Regression equations obtained according to the mixture design of SAS were usedto mix CO2, O2 and N2 to get the desired modified atmosphere. To find the suitableoxygen concentration for the fresh ready retail pork, single factor test was applied.Among the 5, 15, 25, 35, 45 and 55% O2 along with 20% CO2 containing atmospheres,the 45% O2 exhibited stable and satisfactory color scores of the meat during 8 daysstorage study. In addition, it had significantly lower Thiobarbituric acid reactivesubstances (TBARS) value (0.525mg malondialdehyde/kg meat) than that of 55%O2containing package; while total plate count (TPC) (6.11 log cfu/gm) and total volatilebase nitrogen (TVBN) (9.7mg/100gm) values of 45% O2 did not differ significantlyfrom that of 55% O2 containing packs. Similarly, to find the suitable carbon dioxideconcentration for the fresh pork packaging single factor test was applied keeping the45%O2 in each pack. Among 0%, 5%, 10%, 15%, 20% and 25%CO2 concentrations,the 20 and 25%CO2 atmospheres exhibited the best effects for color, lipid oxidationand microbial counts. These two levels 20 and 25%CO2 did not differ significantly. Tooptimize the gas concentrations, orthogonal test was carried out using three levels ofCO2 and O2. In the factorial test, comprising 10-20% level range for CO2 and 35-55%level range for O2, only linear effect of CO2 on the color, TPC and TBARS values wasobserved. In all the cases (responses) the higher the concentration of CO2, the betterwas the result. On the other hand, there were quadratic and linear effects of O2 on thecolor, TPC and TBARS values; however, the quadratic effect was relatively lower. Inaddition, O2 had positive impact on color and microbial count reduction, but hadnegative impact on lipid oxidation. There was no quadratic-quadratic interactioneffect of O2. Thus, the highest level of CO2, that is, 20% and the middle level of O2,that is, 45% were chosen to be most appropriate in the context. As the hot boned meat is sensitive for contamination, lactic acid wasapplied to decontaminate the fresh meat prior to packaging in modified atmosphere.Lower concentrations such as 1% and 2% lactic acid had little effect on microbial loadreduction; on the other hand, 4% and 6% lactic acid exhibited 1 log reduction in TPC,unfortunately it caused significant (P<0.05) negative impact on color and lipidoxidation during storage of meat for 12 days. To reduce the negative effect of lacticacid various concentrations of ascorbic acid was applied. Concentration of ascorbicacid at 1% exhibited the best effect to ameliorate the effect, however couldn't meet thelevel of the MAP packed untreated meat. The higher concentrations 2% and 3% couldnot improve the color. To enhance the color acceptability of the fresh meat, 90%oxygen treatment was also carried out prior to packaging in the MAP; however, itcouldn't exhibit satisfactory effect. Four and 8h oxygen pretreatments exhibited lossof color during storage of the samples; and 16h pretreatment, on the other hand, wasthe best among the treatments, however, it also didn't seem better than the sample keptin the atmosphere containing 45%Oxygen and 20%CO2 without O2 pretreatment. While evaluating the benefit of early packaging of the fresh meat over theconventional post mortem storage prior to modified atmospheric packaging, therewere mixed type of effects. On color and TBA values, early 6hrs postmortem stored xiSouthern Yangtze University, MSc Thesis MAP of fresh porksamples exhibited...